I got the tvc-guide-stationid (64241) from the first post in this thread.
I also noted in my post with links, that I only tested them on tvOS, not Fire OS or AndroidTV.
I've also since switched what happens when I choose MSNBC. Instead of launching the MSNBC app, which is a bit flakey, as described above, I'm having it launch YouTube TV instead.
#EXTINF:-1 channel-id="msnbc" tvg-chno="6050" tvc-guide-stationid="64241",MSNBC
app://com.google.ios.youtubeunplugged
Of note: This solution requires me to manually pick MSNBC once I'm in the YTTV app, but since that's the only channel I've dedicated to that app, and it's frequently watched, it's generally the first thumbnail, so I don't mind.
If I wanted it to launch the NBC app instead, I'd use this one:
#EXTINF:-1 channel-id="msnbc" tvg-chno="6050" tvc-guide-stationid="64241",MSNBC
nbctve://live/msnbc